KAP 140 manual electric trim

[jwx96]

There's always been a delay of about 2-3 seconds from the time I activate the manual electric elevator trim switch on the yoke and when I see the trim wheel actually moving. It's been the same way for my 6 years of ownership. I've always just assumed that was normal and used the trim wheel instead. Is that normal for the KAP 140? Yesterday I flew to a destination 1 hr away and back. On the outbound leg the manual electric trim switch didn't work at all. I started from a heated hangar. Also, when I was climbing and descending with the autopilot I didn't see the trim wheel move. There were no abnormal indications on the KAP 140 display. I didn't turn off the avionics or engine when I was on the ground at my destination and on the return trip everything was back to normal (with the usual 2-3 second delay). Does this sound more like a mechanical/lubrication problem or an electronic connection/servo problem? I'm going into my avionics shop in February for some unrelated work and I can see what they say, but I'm hoping to gain some additional insight first.

[Steve]

John - I have the KAP 140 and there is no lag or delay on activation of the electric trim. Couple of things come to mind:

- Intermittent electrical issue - the trim microswitches could be dirty or having intermittent contact for another reason. That assembly is insanely expensive, and your avionics shop may not be willing to to do a component level repair (i.e. replace the bad microswitch). Of course, the Hangar Fairy could always do it...

- Slipping trim servo clutch - should happen all the time or not at all, but who knows? There is an adjustment procedure if this is the issue.

- Bad trim servo - expensive to replace.

- Dirty trim tab damper rod - I'd bet on this (and luckily this is the cheapest and easiest to fix).

Let us know what the final diagnosis is.

[Diamond_Dan]

There is no lag or delay in activation for the electric trim on my airplane either. Steve gives a good list of suspects and I have a couple of comments. Fortunately I have a KAP guru nearby at KHYA (Griffin Avionics). Other shops in the region will often defer to them for issues.

The trim switch assembly is no longer available. I am told they can fetch upwards of $2K on the used market If you can find one. Mine has stopped working in one direction or the other (one time each way). First time Griffin took it apart and made a manual adjustment. Second time was fixed with contact cleaner. The failure mode in both cases was that it would move in one direction but not the other (by the manual switch). The issue was intermittent until it wasn't. A/P driven automatic trim continued to work just fine in either case.

If you have a dirty trim damper rod, it can be cleaned in a few minutes with some IPA and a wipe. Do NOT apply lubricant to the shaft.

Be careful in this situation. I had a failing elevator trim servo once and the A/P continued to fly out of trim. You can get a surprise when the A/P disconnects and your airplane climbs or dives suddenly.

[jwx96]

Thanks Dan and Steve. I am aware of risk of the autopilot flying the plane in an out of trim condition, and tested for that. Fortunately that doesn’t seem to be happening, but I plan to keep an eye on it. I have some experience flying with an autopilot in an out of trim condition from a previous plane with an STec 30 that didn’t have automatic trim.